1. Field of the Invention
The present invention relates to both a brushless motor including stator core for spinning/driving disks such as hard disks, optical disks, or the like and to a disk drive mounting this brushless motor thereon.
2. Brief Description of Related Art
A brushless motor including stator core generally comprises a stator, which is a stationary part, and a rotor, which is a part that rotates relative to the stator. More specifically, the motor comprises a motor shaft, a rotator, an annular magnet for driving the motor, a stator core, and a motor base. The rotator is supported rotatably about the motor shaft. The annular magnet is attached around the periphery of the rotator and rotates with the rotator as a unit. The stator core faces the annular magnet with a small gap, and a plurality of coils for driving the motor are wound around some parts of the stator core. The motor base supports the motor shaft either rotatably or fixedly, and mounts the stator core thereon.
This type of brushless motor including stator core is widely used as a rotary drive for electronic devices. When applying this type of brushless motor to a disk drive in which disks such as hard disks or optical disks are attached on the rotator at the rotor side, thin brushless motors including stator core and thin disk drives are required. In one example, a stator core is attached on a motor base. The stator core has a plurality of teeth protruding from an annular portion of the core, the teeth facing an annular magnet with a small gap, the magnet used for driving the motor and attached around the periphery of the rotator. A portion of each of a plurality of coils for driving the motor wound around the plurality of teeth enters a corresponding one of a plurality of coil relief holes used for allowing coils to escape. See, for example, Japanese patent application: Publication No. H5-38115 (hereinafter referred to as patent document 1) and Japanese patent application: Publication No. 2006-196139 (hereinafter referred to as patent document 2).
A brief explanation will be given of a spindle motor disclosed in the patent document 1 cited above (Japanese patent application: Publication No. H5-38115). Figures are not shown herein and the explanation will be given while referring to the patent document 1. This spindle motor comprises: a shaft member of which one end fits into a cylindrical part entered from the approximate center of a motor base (base plate); a hub rotatably supported by the shaft member via a shaft bearing; a rotor magnet fixedly attached around the outer surface of the hub; a stator core attached on the motor base, the core facing the rotor magnet; and a plurality of coils for driving the motor, the coils wound around the stator core, wherein a plurality of holes (windows) for allowing the coils to escape are provided at a predetermined pitch along the circumferential direction on the motor base. By allowing a portion of each of the plurality of motor-drive coils wound around the stator core to enter its corresponding hole used for allowing the coils to escape, the length of the spindle motor along the shaft can be shortened, i.e., a thinner motor can be provided without reducing the thickness of the motor base.
Further, a brief explanation will be given of a disk drive disclosed in the patent document 1 cited above (Japanese patent application: Publication No. 2006-196139) while referring to the patent document 2 (figures are not shown herein). This disk drive comprises: a motor base; a cylindrical bearing supporter disposed at approximately at the center of the motor base; a bearing held inside the bearing supporter; a stator core disposed circumferentially around the bearing supporter; a rotating shaft supported by the bearing; a turntable fixed on the rotating shaft; an annular rotor yoke disposed external circumference of the turntable; an annular magnet disposed in the rotor yoke, facing to the stator core; and a disk holder disposed at the center of a surface, the surface being on the other side of the surface that faces the motor base. By providing a plurality of holes (openings) for allowing a portion of each of the coils wound around the stator cores to enter, it becomes possible to make the motor base lighter and to make the whole device lighter and thinner.
A brief explanation will now be given of a conventional brushless motor including stator core to which the technical approach described in patent document 1 and 2 is applied and of a disk drive on which this conventional brushless motor is mounted while referring to FIG. 1˜FIG. 3.
FIG. 1 shows a vertical cross-sectional view along with the O-X2 line indicated in FIG. 2 in order to explain a conventional brushless motor including stator core. FIG. 2 is a bottom view of a conventional disk drive mounting the conventional brushless motor thereon. FIG. 3 is a schematic vertical cross-sectional view of the conventional brushless motor, illustrating a state where the motor base is deformed when an acceleration is given to the direction along the trajectory of the head, which is perpendicular to the motor shaft.
The conventional brushless motor 100 including stator core is configured to be thin so as to be suitable for driving disks as shown in FIG. 1 and FIG. 2.
The conventional brushless motor 100 is disposed and attached at a proper position in a housing 121, which forms the exterior appearance of the conventional disk drive 120, the position corresponding to the trajectory of the magnet head 124, which will be described later. Further, a disk D is rotatably mounted on the brushless motor 100.
In the case where a hard disk is used as the disk D, the magnetic head 124, fixedly attached on the tip of an arm 123 swingably supported by an arm-holding shaft 122 provided in the housing 121, moves in a radial direction so that information signals are recorded or replayed by the magnetic head 124 to/from the hard disk.
As shown in FIG. 1, the conventional brushless motor 100 comprises a stator S, which is a stationary part, and a rotor R, which is a part that rotates relative to the stator S.
First, in the conventional brushless motor 100 described above, at the stator S side, which is a stationary part, a motor base 101 is formed using, for example, an electrolytic zinc-coated steel plate, into a flanged concave-cup shape including: a cylindrical part 101a protruding upward at the center of the plate; a concavely-cupped part 101b that connects to the external circumference of the cylindrical part 101a and recessed downward in the shape of a concave cup; and an annular flange 101c surrounding the concavely-cupped part 101b and protruding upwards.
As shown in FIG. 1 and FIG. 2, on the concavely-cupped part 101b of the motor base 101, a plurality of rectangular-shaped coil relief holes 101b1 for allowing the coils to escape are bored, the coil relief holes penetrating the base and being almost equally angularly-spaced along the circumference. In case the coil-drive phase of the motor drive coil 104 is, for example, three and the motor has nine slots, nine coil relief holes 101b1 are bored onto the base.
Assuming one coil relief hole 101b1 of the nine coil relief holes 101b1 is formed on the line O-X2 passing through the center O of the motor shaft 108 and disposed at the magnetic head 124 side on the motor base 101, then the one coil relief hole 101b1 formed on the line O-X2 generally lies along the direction of the trajectory of the magnetic head 124.
A ring-shaped bearing member 102 is fit into the cylindrical part 101a formed at the center of the motor base 101. On the internal surface of the bearing member 102, fluid dynamic pressure grooves 102a and 102b are separately formed at an axially-upper position and at an axially-lower portion in the axial direction, respectively. For the fluid dynamic pressure grooves, for example, a haring-bone shape can be adopted.
Further, on the external circumference of the concavely-cupped part 101b of the motor base 101, a stator core 103 is fixedly mounted. The stator core 103 is formed by a laminated structure of, for example, silicon steel sheets. An annular portion 103a of the core is formed on the outer side of the stator core 103, and on the annular portion 103a, nine equally circumferentially-spaced teeth 103b are formed radially inwardly.
Around each of the nine teeth 103b formed on the stator core 103, a motor drive coil 104 is wound, and a portion of each of the nine motor drive coil 104 enters one of the nine coil relief holes 101b1 fused or allowing the coil to escape formed on the concavely-cupped part 101b of the motor base 101, by which, the brushless motor 100 is made to be thin.
Next, on the rotor side R described above, motor shaft 108 made of stainless steel is fixedly attached in the center hole 107a bored at the center of the rotator made of aluminum (herein after referred to as “rotor hub” 107). This motor shaft 108 rotatably fits into the fluid dynamic pressure grooves 102a and 102b of the bearing member 102 on the stator S side. On the lower end of the motor shaft 108, a thrust plate 105 at the stator side that bears the thrust load and a support plate 106 that strengthens the thrust plate 105 are attached.
The upper portion of the bearing member 102 provided at the stator S side faces a backside center concave part 107b formed concavely in the center of the backside of the rotor hub 107.
Around the external circumference of the rotor hub 107, the small-diameter part 107c is formed at the lower position, the large-diameter part 107d is formed above the small-diameter part 107c, and medium-diameter part 107e is formed above the large-diameter part 107d. 
Around the external circumference of the small-diameter part 17c of the 17, a motor-drive annular magnet 109 is fixedly attached, and nine teeth 103b formed on the stator core 103 face the motor-drive annular magnet 109 with a small gap.
The lower disk D is mounted on the large-diameter part 107d of the rotor hub 107. Above the lower disk D, an upper disk D is mounted via an annular spacer 110 fit in the medium-diameter part 107e of the rotor hub 107, the upper disk D being held by a clamp 111. Further, the clamp 111 is fixed on the motor shaft 108 by a screw 112.
When operating the conventional brushless motor 100 configured as described above and recording/retrieving information signals to/from the disk D using the magnetic head 124, swingably supported by the arm-holding shaft 122 disposed in the housing 121, provided no external jolting or shaking is given to the conventional brushless motor 100, the magnetic head 124 can be positioned on a desired track on the disk D, i.e., the magnetic head 124 is on track.
However, as shown in FIG. 3, in the case where an external jolting and/or shaking is given so that acceleration FA in the direction of the trajectory of the magnetic head 124, which generally intersects with the motor shaft 108 at a right angle, is given, since the one coil relief hole 101b1 of the plurality of coil relief holes bored onto the concavely-cupped part 101b of the motor base 101 is formed generally along the direction of the trajectory of the magnetic head 124 (direction O-X2) as described above, the motor base 101 is skewed generally in the direction of the trajectory of the magnetic head 124 by the acceleration FA described above. This skew causes displacement in the relative position between the disk D and the magnetic head 124, and, thus, the magnetic head 124 is positioned off the desired track on the disk D, i.e., the magnetic head 124 is off-track. As a result, the information data may not be retrieved or recorded properly.